1. Field of the Invention
The invention relates to ventricular catheters and more particular to multimodal catheters for focal brain monitoring and ventriculostomies.
2. Description of the Related Art
External ventricular drainage catheters are known in the art. External Ventricular Drainage (EVD) catheters are indicated for drainage of cerebrospinal fluid (CSF) from the lateral ventricles of the brain and for relieving intracranial pressure. A typical EVD catheter has a length of fifteen to thirty-five centimeters (15-35 cm) with an outer diameter between two and one half and three and three tenths millimeter (2.5-3.3 mm) and an inner diameter between one and three tenths and one and nine tenths millimeter (1.3-1.9 mm). A stylet is typically used for inserting the distal end of the EVD catheter into the brain tissue and a trocar is used for the proximal subcutaneous insertion. A Luer connector can be added at the proximal end of the EVD catheter. Easy to see length depth markers have been taught for aiding in quick insertion. EVD catheters exist that are translucent with a barium impregnated stripe allowing for both immediate visualization of CSF and radio-opacity. A number of lateral holes are included to allow the CSF to enter the EVD catheter.
Prior-art EVD catheters are typically inserted according to the following procedure. The patient is given a local aesthetic at the location of insertion. A first incision is made in the skin on the head at the location of insertion. The skull is drilled. The catheter is then inserted to a depth of five and five tenths to six centimeters (5.5-6.0 cm) to reach the lateral ventricle. CSF under pressure from cranial injury, inflammation, hemorrhage, or the like can be vented externally by the EVD catheter. To prevent infection, a second incision is made in the skin, the EVD catheter is tunneled to the second incision and the first incision is closed. The tunneling procedure closes a direct opening to exposed brain.
Monitoring, in particular continuous monitoring of the brain tissue surrounding an injury has been found to be an important diagnostic tool. See Zauner, Alois et al., “Instruction for Continuous Multiparameter Monitoring of Substrate Delivery and Brain Metabolism;” and Zauner, Alois, “Brain Tissue Monitoring in Critical Neurosurgical Patients: User Guide for the Neurotrend in the ICU and during Critical Cerebrovascular Surgery.”
When a ventriculostomy is performed, the insertion of the EVD catheter creates microhemorrhages in the surrounding brain tissue. The microhemorrhages change some of the qualities of the brain tissue. The microhemorrhages range between two and four hundred microns (2-400 μm) deep into the tissue. Measurements made by various sensors or catheters in the tissue having microhemorrhages have been found to be inaccurate and not characterize the underlying brain tissue.
Sensors have been used with EVD catheters. These sensors are generally threaded coaxially with the EVD catheter. That is, the sensors extend alongside the EVD catheter. Therefore, the sensors are measuring the damaged tissue surrounding the EVD catheter and not undamaged neighboring brain tissue.
Placing sensors on an opposing side from an EVD catheter to avoid microhemorrhages created by EVD catheter insertion is not recommended. Insertion catheters into both hemispheres of the brain can lead to loss of speech and/or memory.
Another problem with the prior art is the connectors for the sensors. The prior art uses large plastic or metallic bolts to connect the sensors to the corresponding leads and monitors. The bolts are bulky (approximately, 5 cm by 4 cm by 1 cm) and have no means for connecting to the EVD catheter. Patients often move, brush, or even remove the bolt accidentally. In addition, the bolt's weak connection fails to prevent infection.
Another problem with the prior-art EVD systems is that the sensor cannot be added subsequent to the insertion of the EVD catheter. The sensor or sensors in prior-art systems are inserted simultaneously with the EVD catheter and alongside the EVD catheter. Therefore, once the EVD catheter is inserted, additional sensors cannot be added without removing the EVD catheter and inserting a replacement. In addition, surgeons avoid using all of the possible sensors with every EVD catheter because the sensors are often very expensive so using them without a specific reason is prohibitive. Manipulating the EVD catheter and/or sensors once they are placed requires reopening of the incision and this significantly increases the infection risk.
A related problem is that the sensors are only approved to be inserted for four to seven days. This time is frequently less than the desired insertion time for EVD catheters. Many critical patients have EVD catheters that remain inserted for more than ten days. Therefore, there is a need in the prior art to provide a means for adding sensors and catheters independently of the insertion of the EVD catheter.
An additional problem with the prior art is that the sensor is added coaxially along with the EVD catheter. As the number of sensors and catheters increases, the total cross section increases. Of course, when brain tissue is being damaged, an object is to affect as little as possible. Accordingly, an object of the invention is to provide a system that allows sensors and catheters to be included while consuming a minimal cross section.